The present invention relates to an extraction device for removing an injection molded substrate from an injection mold, and to an injection molding machine provided with an extraction device. Such devices and machines are useful in the production of optical data carriers, such as CD, CD-R, DVD, DVD-R, single-CD, OBC, and the like.
European patent publication no. EP 0 205 152 A2 and German patent publication no. DE 2414741 disclose a gripper for removing an injection molded substrate from an injection mold, wherein the gripper has rubber suction cups and can be pivoted in and out in relation to the opened injection mold. The gripper is moved close to the injection molded substrate, so that the suction cups come into contact with the injection molded substrate. A vacuum is produced in the suction cups, causing the substrate to adhere to the suction cups. The gripper then moves away from the half-mold that holds the substrate by an axial distance sufficient to remove the injection molded substrates from the half-mold. The gripper is then pivoted out of the region of the injection mold and rotated so that the substrate can be transferred to the following processing station in a horizontal orientation.
Grippers with suction cups used heretofore, however, are not capable of quickly removing the substrate from the injection mold to the outside, because the attainable pivoting speeds depend on the holding power of the suction cups. The inertial forces produced by a rapid pivoting motion can be so great that the substrates can slip off the suction cups entirely and drop down, or at least shift, so that the substrates can no longer be transferred to the following processing stations with the required positioning accuracy. This limits an achievable improvement in the cycle time, which is important for an economical production of optical data carriers.
Typically, the manufacture of substrates for optical data carriers involves a supply of plastic material, after melting in a plasticizing unit, in the center of the substrates through a sprue channel that extends perpendicular to the substrate plane. The plastic melt is hereby introduced in the region of the later opening in the center of the substrate and uniformly distributed across the periphery of this opening into the mold cavity. The sprue formed during the injection molding process in the sprue channel must be separated from the substrate after the cool-down phase and removed.
German patent publication no. DE 28 38 634 discloses a process for making a ring-shaped article by an injection molding process, whereby the sprue that is connected with the article is punched out inside the injection mold from the injection-molded article and expelled by an sprue ejector. The manufacture of substrates for optical data carriers of the afore-described type places stringent demands on precision and cleanliness. For this reason, producing the central openings by punching out the sprue in the injection mold carries significant risks.
To address this problem, German patent publication no DE 35 26 632 C2 proposes to form a substantial part of the opening in the substrate in axial dimension already during the injection molding process. The connection zone between the substrate and the sprue can be made small enough for the cross-section to allow plastic melt to pass through. The sprue hereby protrudes in the axial direction slightly beyond the substrate in the connection zone. The axial offset and the diameter of the sprue part protruding beyond the substrate are selected so that during separation of the sprue from the substrate a separation edge is formed that is inclined at an angle of 45° relative to the plane of the opening in the substrate, whereby the injection-molded article amounts to 70% of the axial length of the opening and the part being separated amounts to 30% of the axial length of the opening. After the cool-down phase, the sprue is held by an undercut in a sleeve that can axially move in the mold, with an ejector being axially movable in the sleeve. The sprue is separated along the narrow separation edge from the substrate by retracting the sleeve. The sleeve is then moved farther to the back, until the sprue reaches the region of an opening in the injection mold. By moving the ejector forward, the sprue is pushed out of the sleeve and can drop out of the injection mold through the opening. The substrate is removed by rotating a gripper into the open injection mold. The gripper is provided with rubber suction cups that are applied outside the information-carrying area of the optical data carrier, in particular inside the so-called clamping region. The substrate can also be pushed into an outlet channel after demolding. The outlet channel is less suitable for the removal of substrates for optically readable business cards (so-called OBC=Optical Business Card) due to their rectangular shape.
However, for a number of reasons, this proposal is also endowed with drawbacks and shortcomings because the described separation at a separation edge cannot prevent formation of dust.
It would therefore be desirable and advantageous to provide an improved extraction device for removing an injection molded substrate from an injection mold, in particular substrates for optical data carriers, to obviate prior art shortcomings and to allow a rapid pivoting motion, without risk that the substrate shifts or even detaches during the pivoting motion.
It would also be desirable to provide an improved injection molding machine, in particular for manufacturing a substrate for optical data carriers, to obviate prior art shortcomings and to attain short cycle times while entirely eliminating the risk of dust formation inside the injection mold.